1. Field of the Invention
The present invention relates to a nonaqueous electrolyte secondary battery. In more detail, the present invention relates the battery in which an operation upper limit potential of a positive electrode is set to 4.3 V or more based on metal lithium.
2. Description of Related Art
Since a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery has weight lighter and energy density higher than a conventional battery, it is preferably used in a so-called portable power source, an on-vehicle high output power source, and the like.
Now, in the nonaqueous electrolyte secondary battery, as part of performance improvement, it is under study to achieve higher energy density. Such a higher energy density can be realized by setting, for example, an operation potential of the positive electrode higher than ever before. However, when an operation upper limit potential of the positive electrode is set to, for example, about 4.3 V or more based on metal lithium, in consequence of high potential of the positive electrode, the battery characteristics (typically, endurance, for example, cycle characteristics) may deteriorate. As a technique relating to this, Japanese Patent Application Publication No. 2003-173770 (JP 2003-173770 A) is cited. JP 2003-173770 A describes to the effect that a decomposition reaction of a nonaqueous electrolyte in a high potential state can be suppressed from occurring and self-discharge and battery swelling during exposure to high temperature can be reduced by coating a surface of particles of an active material with lithium ion conductive glass.